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block, bfq: fix queue removal from weights tree

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bfq maintains an ordered list, through a red-black tree, of unique
weights of active bfq_queues. This list is used to detect whether there
are active queues with differentiated weights. The weight of a queue is
removed from the list when both the following two conditions become
true:

(1) the bfq_queue is flagged as inactive
(2) the has no in-flight request any longer;

Unfortunately, in the rare cases where condition (2) becomes true before
condition (1), the removal fails, because the function to remove the
weight of the queue (bfq_weights_tree_remove) is rightly invoked in the
path that deactivates the bfq_queue, but mistakenly invoked *before* the
function that actually performs the deactivation (bfq_deactivate_bfqq).

This commits moves the invocation of bfq_weights_tree_remove for
condition (1) to after bfq_deactivate_bfqq. As a consequence of this
move, it is necessary to add a further reference to the queue when the
weight of a queue is added, because the queue might otherwise be freed
before bfq_weights_tree_remove is invoked. This commit adds this
reference and makes all related modifications.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2019-01-29 12:06:34 +01:00 committed by Jens Axboe
parent d87447d84f
commit 9dee8b3b05
2 changed files with 16 additions and 7 deletions
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17
block/bfq-iosched.c
View File

@ -754,6 +754,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
inc_counter:
bfqq->weight_counter->num_active++;
bfqq->ref++;
}
/*
@ -778,6 +779,7 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd,
reset_entity_pointer:
bfqq->weight_counter = NULL;
bfq_put_queue(bfqq);
}
/*
@ -789,9 +791,6 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
{
struct bfq_entity *entity = bfqq->entity.parent;
__bfq_weights_tree_remove(bfqd, bfqq,
&bfqd->queue_weights_tree);
for_each_entity(entity) {
struct bfq_sched_data *sd = entity->my_sched_data;
@ -825,6 +824,15 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
bfqd->num_groups_with_pending_reqs--;
}
}
/*
* Next function is invoked last, because it causes bfqq to be
* freed if the following holds: bfqq is not in service and
* has no dispatched request. DO NOT use bfqq after the next
* function invocation.
*/
__bfq_weights_tree_remove(bfqd, bfqq,
&bfqd->queue_weights_tree);
}
/*
@ -1020,7 +1028,8 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
static int bfqq_process_refs(struct bfq_queue *bfqq)
{
return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
return bfqq->ref - bfqq->allocated - bfqq->entity.on_st -
(bfqq->weight_counter != NULL);
}
/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */

6
block/bfq-wf2q.c
View File

@ -1673,15 +1673,15 @@ void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfqd->busy_queues[bfqq->ioprio_class - 1]--;
if (!bfqq->dispatched)
bfq_weights_tree_remove(bfqd, bfqq);
if (bfqq->wr_coeff > 1)
bfqd->wr_busy_queues--;
bfqg_stats_update_dequeue(bfqq_group(bfqq));
bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);
if (!bfqq->dispatched)
bfq_weights_tree_remove(bfqd, bfqq);
}
/*